An internal combustion engine is conventionally known that includes a turbocharger, which drives an impeller of a compressor with the energy of exhaust gas (see Patent Document 1, for example).
In an internal combustion engine, blow-by gas in a crank case flows back to the intake passage through a blow-by gas recirculation passage. In the case of an internal combustion engine featuring natural aspiration without a turbocharger, specifically in the case of what is referred to as an NA internal combustion engine, a blow-by gas recirculation passage is connected to the intake manifold and blow-by gas is drawn in with negative pressure generated in the intake manifold.
In contrast, in the case of an internal combustion engine with a turbocharger, a downstream section that is downstream of an impeller in the intake passage is subjected to a pressure increase especially during forced induction. Hence, if nothing is done, blow-by gas cannot flow back to the intake passage.
According to the technique described in Patent Document 1, a bypass passage that bypasses the intake passage is provided in the aforementioned downstream section of the intake passage. An ejector mechanism to generate negative pressure is located in the bypass passage. A blow-by gas recirculation passage is connected to the ejector mechanism. More specifically, a valve to adjust the flow rate of compressed gas to flow into the intake passage and a valve to adjust the flow rate of compressed gas to flow into the bypass passage are arranged in a branching portion of the intake passage, at which the intake passage branches into an upstream section of the bypass passage. The degrees of openings of these valves are controlled to adjust the flow rate of the compressed gas to be introduced into the ejector mechanism through the bypass passage, thereby generating negative pressure in the ejector mechanism. This allows blow-by gas to flow back to the intake passage even during forced induction.
An internal combustion engine with a turbocharger includes an air bypass passage connecting a downstream section and an upstream section of an intake passage with respect to an impeller and an air bypass valve that adjusts the flow rate of compressed gas to flow back through the air bypass passage. The degree of opening of this valve is controlled to adjust the flow rate of the compressed gas to flow back to the upstream section of the intake passage. This suppresses generation of surging of the compressor when the throttle valve is closed.